Three-phase transformer



March 13, 1951 D. E. WIEGAND 2,544,871

THREE-PHASE TRANSFORMER Filed April 24, 1947 5 Sheets-Sheet l INVENTORDAVID E. WIEGAND /ZZGA: v

ATT NEY March 13, 1951 D. E. WIEGAND THREE-PHASE TRANSFORMER 5Sheets-Sheet 2 Filed April 24, 1947 INVENTOR DAV-ID E.W|EGAND a/F kATTORNEY March 13, 1951 D. E. WIEGAND THREE-PHASE TRANSFORMER 5Sheets-Sheet 3 Filed April 24, 1947 INVENTOR DAVID E.WlEGAND March 13,1951 D. E. WIEGAND THREE-PHASE TRANSFORMER Filed April 24, 1947 5Sheets-Sheet 5 lNVENTOR DAVID E.WIEGAND BY QZM ATTORNEY Patented Mar.13, 1951 THREE-PHASE TRANSFORMER David E. Wiegand, Villa Park, Ill.,assignor to McGraw Electric Company, a corporation of DelawareApplication April 24, 1947, Serial No. 743,568

This inventionrelates to three phase transformers and is particularlydirected to the core construction for a three phase transformer.

In three phase transformers where the cores are formed of wound magneticribbon, it has been found extremely difiicult to adequately provide forthe transfer of flux from one core section to another core section evenwhere a skew type wound core construction is employed, as shown in mycopending application, Serial No. 556,546 filed September 30, 1944, forThree Phase Transformers, which is now abandoned. This limitation in thepath of flux which prevented all of the flux through one conductingwinding assembly from getting into another conducting winding assemblywithout part of the flux transferring from one core section to anothercore section produced a certain amount of core loss. My above notedcopending application is owned by the same assignee as that of thepresent application. In my above noted. prior application, thetransformer was made by winding three closed cores of magnetic ribbonand skewin or staggering the three successive layers of magnetic ribbonin these core sections so that there was substantially an edge to edgecontact between the laminations of the successive cores where they passthrough the conducting winding assemblies. In order to adequately fillthe circular windows in the conducting winding assemblies, it wasnecessary, as shown in the above copending application, to use differentwidths of magnetic ribbon.

Objects of this invention are to provide a construction of a three phasetransformer core which will materially reduce the three phase core lossdue to flux path limitations in the heretofore known types of threephase wound core transformers, of which my copending applicationhereinabove noted is an example.

A further object of this invention is to provide a core construction ofsuch a nature that it is possible to use the same width of magneticribbon in winding the several cores and yet to so arrange and form thesecores that they substantially fill the circular windows through theconducting winding assemblies.

One way of reducing the core loss in a three phase transformer is to usethe Y or zig-zag connections exclusively'in both the primary andsecondary windings of the transformer. This connection allows theinduced secondary voltage in the three conductin winding assemblies tocontain third harmonic components which will peak the induced voltagewave and which will flatten the flux wave through the core. Therefore,it is clear that for a given value of induced or secondary voltage thepeak flux value is less and the core loss is less than would be the casehad a delta connection been used. This distorted wave shape of voltagedue to the presence of the third harmonic components does not appearbetween secondary lines since the third harmonic components cancel out.It is to be noted also that if a zig-Zag connection is used/the voltagefrom the lines to neutral is not distorted. Even if a Y or zig-zagconnection is used the advantages in reduction of core loss is notobtained in the prior types of three phase trans formers which areenclosed in a tank for the tank surrounds the transformer fairly closelyand tends to produce the effect of a delta connection or a deltatertiary circuit which increases the core loss for a given inducedsecondary voltage. The delta effect of the tank is due to its electricalconducting properties. this, there is a further loss due to the magneticproperties of the tank. Any stray flux which gets into the tank wallwill cause hysteresis and eddy current losses in the tank which willincrease the stray losses of the transformer.

This invention has a still further object of eliminating the harmfuleffect of the surround ing tank, which tank is composed of magneticmaterial.

out having these auxiliary flux paths interlink more than a singleconducting winding assembly, the main body of the core construction,however, providing for the interlink of flux for all of the conductingwinding assemblies. In other words, this invention has a further object,not

; only the provision in a wound core type transthat would have passed tothe surroundingtank and in this manner makes it possible to get the fulleffect of reduced core loss where a Y or zig-zag connection is used forboth the primary and the secondary.

An embodiment of the invention'is shown in the accompanying drawings, inwhich:

Figure 1 is a plan view of the transformer showing a fragment'of thetank and showing parts broken away andin section.

Figure 2 is a view looking from one side of the transformer."

In addition to The invention provides means where by auxiliary fluxpaths are provided for each of the several conducting winding assemblieswith Figure 3 is a view showing the manner in which the ribbon is wound.

Figure 4 is aside view of the structure shown in Figure 3.

Figure 5 shows the ribbon after it has been wound and in positionbetween dies.

Figure 6 shows the manner in which the ribbon is staggered or skewed byclamping the dies together.

Figure 7 is a-View showing another method of winding the ribbon, suchView showing a ribbon being wound in a staggered or skewed manner.

Figure 8 is a face view of an auxiliary core.

Figure 9 is a face view of a main core.

Figure 10 is a side elevationof Figure 9.

Figure 11 is a top view of Figure 9.

Figure 12 is a sectional view on the line I2--i2 of Figure 9. H

Figure 13 is a vector diagram showing the fiuxes common to two coils.

. Figure 14 is a vector diagram showing the fluxes linkingonly one coil.

Figure 15 is avector diagram showing the total fluxes in one "coil.

Figure '16 is a diagrammatic view showing a Y Y connection of theconducting 'windingassemblies.

Referring to the drawings, it will beseen that three main cores havebeen indicated by the reference characters 1, 2, and 3 and the threeauxiliary cores by the reference characters 4,-5, and fi. The conductingwinding assemblies are indicated bythe reference characters 1, 8, and-9and the tank by the referencecharac'er iii.

In making the transformer the conducting winding assemblies are-wound inplace and'are circular-and have circular windows indicated in Figure 2by the reference character 8 I The conducting winding assemblies, ineach instance, include-a primary and a secondary. The primary windingsare indicated in- Figure 16 by the reference character P and thesecondary windings by the reference character S. It is preferable toconnect the primaryand secondary both in-Y relation on in zig-zagrelation for a reason hereinafter to appear. Though this invention, inits broadest aspects, -is not limited to either of these connections forif desired delta connection could be used though it ispreferable to usethe other type of connections hereinabove set forth.

The main cores and the auxiliary cores are each formed in exactly thesame manner though it is noted froma comparisonofFigures 8 and 9; whichshow respectivelyan auxiliary core and a main core that'the rectangularwindows l2 and I3 in the auxiliary and main cores'are of diiferent'sizes, the windowiiz of the auxiliary core being materiallysmaller thanthe-window I3 of the main core. The reason for thisis that the main coreinterlinks two conducting Winding assemblies and the auxiliary corelinks only one conducting winding assembly. This is shown very clearlyin Figures land 2.

Informing the cores, one has been-selected,

This is necessary for it has been found that even slight mechanicalstrain in the core sections increases the losses in the actual operationof the transformer.

It is obvious that the core sections could be formed as shown in Figure7 by winding them in a staggeredrelaticn on the mandrel i7 and omittingthe subsequent step of staggering or skewing themby means of dies shownin Figures 5 and 6.

The circular conducting windings'are wound in place I on the compositelegs formed of l the two main cores and the a'uxiliarypore :in eachminstance. -Any suitable' means may be iused 1 for winding the conductingwinding assemblies after the'cores have beenassembled. For example,- thewinding machine disclosed in thepatent to'.'Stein mayer et al., No.2,305,999 of December-22,31942, for Method .and lvlachine for WindingCoils could be used.

The vector diagram for the fluxes in the main cores 'are indicatedby'the reference characters A, B, and C in Figure 13, while the vectordiagram for the fluxes 'in theauxiliary cores areshown at A1, B1; and'Cr in Figure 14. 'The 'combined -flux interlinking any givenconducting:winding assemblyis indicated at Din Figure 15. alt'will beseen that this vectorDis arrived atsby subtracting thevector B from thevector A and"addin'g the vector A1 of the-auxiliary core.

This invention .is an improvement-1 over that disclosed in my copendingapplication z 'herein- This core is shownas being wound on'a above notedand it is designedto materially reduce the core losses evenover thatforatransformer built in accordance with the disclosure of my above notedcopending application. *The'core'loss in the three phase transformerisreduced-when a -V or zig-zag connection-is used forbbththe primary andthe secondary of'ithetransformer. This connectionpermits"inducedsecondary=vo'1tage in the three coils to containthird-"harmonic components which peak the induced voltage'wave.

However, this third harmonic .flattens'zthe'fiux wave. Therefore, for agiven value-bf induced voltage the peak value of the flux is le'ssand.consequently the core 'loss is less. Further it' is to be noted that byusingaY"connectionor& a gig-nag connectionthe third iharmonicfdoes'notappear between lines as thethird' harmonics'are cancelled out. If-a-zig-zag-'connection insed, the voltage from lines to neutraldoes"nothave the third harmonic.

It has been found that wherea wound-core type of transformer --isconstructed in accordance with the disclosure ofmy'*above'-noted-copending application that the'tank which 'encirclesthe transformer acts like a delta connected winding or a tertiarydeltaconnected"winding and, therefore, the advantages of the Y-onzig'zagconnection in reducing the careless" for-*a'thre phase transformerisnot'obtained. =However by providing the auxiliary cores 'whichfurniswavery low reluctance flux path" independenti ot-tlie common flux pathsforeach conducting "winding assembly, the unclesirable effect of thetank- 'wall is avoided. It is, therefore, possible to use a Y connectionor zig-zag connection and obtain the maximum reduction in core loss asall of the advantages of a Y connection or zig-zag connection areobtained though the transformer is surrounded by the tank. In additionto this, the losses due to the magnetic properties of the tank areavoided, as practically no stray flux gets into the tank wall.

Another very pronounced advantage is obtained by the peculiar manner inwhich the main and auxiliary cores are staggered or skewed and areassociated with each other. It is to be noted that the main cores I, 2and 3 are all staggered inwardly and the adjacent edges of the magneticribbon are positioned in close juxtaposition or substantial edge to edgecontact with each other. The auxiliary cores are also staggered orskewed and their tapered or staggered edges are positioned adjacent orin substantial contact with the flat face of the main core, whereas,their fiat faces are arranged in back to back relation with another ofthe main cores. Thus it will be seen from an examination of Figure 1that each auxiliary core lies in the same general plane as thecorresponding main core and a symmetrical arrangement of cores isobtained. The arrangement is such that although the same width ofmagnetic ribbon is used throughout for both the main and auxiliarycores, nevertheless, a hexagonal cross-sectional contour is obtained forthe composite leg formed of two main cores and the auxiliary core whereit passes through a conducting winding assembly. In this way, anexcellent space factor is obtained which compares very favorably withthe previously used cruciform cross-sections for wound magnetic cores.It is, of course, apparent that if desired, sections of different widthscould be employed for the magnetic ribbon, but only a very slight gainin space factor would be obtained which would not warrant the additionalexpense necessitated by the use of different widths of ribbons. Insteadof the additional expense due to using different widths, ribbons of asingle width are used throughout as stated hereinabove and yet anexcellent space factor is obtained.

The expression star connected as used in the claims hereinafter appendedis intended to cover either a Y connection or a zig-zag connection ofthe conducting winding assemblies and is used to distinguish from adelta connection.

It is to be noted particularly that each of the adjacent pairs of maincore sections when combined with an auxiliary core section form jointlya winding leg about which the conducting winding assembly is wound asdescribed in detail hereinbefore. The construction readily lends itselfto winding circular conducting winding assemblies around the Winding legas each core section has straight leg portions which, as statedhereinabove, form jointly the winding legs of the transformer.

Although this invention has been described in considerable detail, it isto be understood that such description is intended as illustrativerather than limiting, as the invention may be variously embodied and isto be interpreted as claimed.

I claim:

A three phase transformer comprising three conducting windingassemblies, three main cores and three auxiliary cores, the three maincores being arranged in the shape of a triangle, each of the three maincores interlinking only two conductin winding assemblies, a metal tanksurrounding said transformer, said conducting winding assemblies havinga star connected primary and a star secondary winding, the auxiliarycores each linking a single and a different conducting winding assemblyand providing independent flux paths of low reluctance and arranged. toprevent the delta effect of the surrounding tank, the portions of saidmain cores which interlink a common Winding assembly having asubstantially edge-to-edge contact with each other and the auxiliarycores each having a substantially edgeto-face contact and a back-to-backcontact with the adjacent main cores.

DAVID E. WIEGAND.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 523,572 I-Iassler July 24, 18941,390,050 Lee Sept. 6, 1921 1,766,654 Kubler June 24, 1930 1,780,110Bliss Oct. 28, 1930 2,220,732 Sanders Nov. 5, 1940 2,355,169 Lehman etal Aug. 8, 1944 2,401,952 Mayberry June 11, 1946 2,408,212 HodnetteSept. 24, 1946 2,458,112 Steinmayer Jan. 4, 1949 OTHER REFERENCES DieWechselstrom Technik, by E. Arnold and J. L. La Cour, Zweiter Band 2Aufiage, Berlin, 1910, pp. 89 to 94.

